The invention pertains to devices for tapping or drilling from a branch line into a main line in a fluid transport system. More particularly, it pertains to a device for tapping into a hot or pressurized natural gas main without venting substantial amounts of gas to atmosphere.
In a natural gas delivery system, a main pipe, such as a street main, is typically buried underground. It is often necessary to connect a branch pipe to the main pipe to, for example, provide service to a newly constructed facility. To do this, the utility must excavate to reveal the main pipe and lay the branch pipe. A base section of the branch pipe having a predetermined length is secured and sealed at its upstream end to the main pipe. A drill may then be inserted through the downstream end of the base section for drilling a hole in the main pipe to permit communication with the branch pipe.
If this process is done while the main pipe remains pressurized, it is referred to as a hot tap (in distinction to a cold tap). In a hot tap, it is desirable that the tapping operation be conducted so as to minimize any discharge of gas to atmosphere for pollution, safety, and cost reasons.
It is additionally desirable that excavation costs and other associated labor costs be minimized and that the operation be conducted with the greatest possible ease. In particular, it is desirable to minimize the excavated space downstream of the base section of branch pipe which is necessary to allow for insertion and removal of the drill shaft from the branch pipe. It is furthermore desirable to minimize the space needed downstream of the pipe for men and equipment used to drive the drill bit both for the application of torque and the application of longitudinal force to bring the bit into engagement with the main pipe.